1. Field of the Invention
This application relates to cable construction. More particularly, the present invention relates to an improved LAN (Local Area Network) cables construction.
2. Related Art
In the field of cable construction, particularly LAN cables, ever advancing bandwidth requirements are requiring new and innovative ways to meet the desired testing requirements. For example, the cabling standard TIA 568-B.2-10 2008 defines augmented category 6 cabling (Cat 6a). This standard defines the parameters for running 10 Gigabit signaling over Cat 6a copper cable (for 10GBASE-T). This standard specifies cabling performance to 500 MHz and includes certain performance specifications and test requirements for internal and Alien Crosstalk, among other electrical parameters.
Typically, in prior art arrangements shorter lay length pairs are used in multi-pair cables to reduce cross-talk. However, shorter lay lengths use more wire per length of cable, and thus there are limitations on how short the lay length can be in any given copper wire twisted pair. Therefore, it is ideal to have the longest lay length possible that meets the desired crosstalk threshold.
In addition to the crosstalk that occurs between pairs within the same sub-group (unit of 4 adjacent pairs), an additional type of interference occurs between twisted pairs of adjacent sub-groups (4 pairs groups) and between pairs of adjacent cables referred to as ALIEN crosstalk. Although crosstalk within a sub-group (4 adjacent pairs) is easier to manage because the lay lengths of the closest pairs can be tightly managed, ALIEN crosstalk is harder to mitigate within the cable itself due to the sub-group (unit of 4 adjacent pairs) proximity.
The ALIEN crosstalk is difficult to predict and mitigate since external cable conditions, such as the number of adjacent cables having the same twist rate from cable to cable; the distance between adjacent cables; longer pair lay length in adjacent cables; unknown lay lengths of twisted pairs in adjacent cables; etc. . . . , can not be easily predicted.
Regarding the application of Cat 6a standards, in particular, in the area of larger 24 twisted pair cables, several different options have been pursued in the prior art. For example, for UTP (Unshielded Twisted Pairs) cables, the 24-unshielded twisted pairs are bundled within the outer jacket into six 4 pair sub-cables, which together are Cat 6a, 10GBASE-T compliant. Such an arrangement is shown in prior art FIG. 1. FIG. 2 also shows a prior art arrangement with six four-pair sub cable having a central filler.
In another prior art arrangement in STP (Shielded Twisted Pairs) cables, to produce a 24 pair Cat 6a 10GBASE-T compliant cable, the twisted pairs are disposed in two concentric layers, the inner having 9 pairs and the outer layer having 15 pairs. Each of these pairs is individually shielded. An example of this design is shown in prior art FIG. 3.
However, in each prior art case, the construction arrangement used to make these cables Cat 6a 10GBASE-T compliant have added significant size (diameter), weight and costs to the cables.
For example, the cable shown in FIG. 1 utilizes a significant amount of additional polymers, such as FRPVC (Flame Retardant Polyvinyl Chloride) for each of the sub-jackets as well as with the larger outer jacket. Not only does this provide an enormous amount of fuel making it difficult to pass fire safety standards, it also adds significant size to the cable making it unsuitable for particular uses. Typically, such prior art cables are approximately 1.0″ in diameter.
One such standard that these types of cables need to meet is the NEC (National Electric Code) fire safety standard for “Riser” rating, abbreviated—CMR. Cables designed as shown in FIG. 1 do not always meet the CMR standards and are poorly suited for risers anyway given their large diameters.
Likewise, the cable shown in FIG. 2, also uses FRPVC and has a typical diameter of approximately 0.8″-0.9.″ Such designs utilize a significant amount of shielding, and also have added fuel (because of the thicker jackets on the pair wires themselves owed to the shielding). Furthermore, 24 separate shielded pairs requires 24 separate ground terminations for the installer, which is undesirable.
In each these two cases, although the cables meet the desired transmission performance ratings, the diameters, weight, cost and other poor design qualities of these cables make them unacceptable for many applications.
In view of these concerns outlined above, prior art cables have implemented many features necessary to meet various transmission performance standards, but in doing so have negatively impacted the traditional physical standards that cables must also meet.